Index: wp-includes/category-template.php
===================================================================
--- wp-includes/category-template.php	(revision 24000)
+++ wp-includes/category-template.php	(working copy)
@@ -370,7 +370,7 @@
 	if ( ! $r['hide_if_empty'] || ! empty($categories) )
 		$output .= "</select>\n";
 
-	$output = apply_filters( 'wp_dropdown_cats', $output );
+	$output = apply_filters( 'wp_dropdown_cats', $output, $r );
 
 	if ( $echo )
 		echo $output;